Below-grade luminaires have been used for lighting trees and architectural features since the 1950's. They are desirable in locations where above-grade lighting fixtures would distract from the landscape design. In areas such as paved pathways and courtyards where trees are located in wells, this is the only luminaire type that will not pose a hazard to pedestrians because the luminaire is flush with the grade level.
Early configurations included a lamp housing and integral junction box accessible at grade level. The visible junction box was not large, and generally not objectionable as seen at grade level. However, High Intensity Discharge (H.I.D.) lamps soon became the desired light source because of their efficiency and long life. But the H.I.D. lamps required a ballast assembly, and therefore a larger box was needed to house the ballast assembly. The visible above-grade footprint of those luminaires became quite large due to the elements which required access for installation and servicing: the lamp housing, the junction box, and the ballast box.
Because of the large visible footprints, below-grade luminaires were reconfigured with the junction box and ballast box located beneath the lamp housing. This solved the objection to the large visible footprints, but created other problems. First, the luminaires became much deeper creating the concern that installation too close to existing landscaping might damage roots. Second, the luminaires became difficult and more time consuming to install because the junction box was located at the bottom of the lamp housing. This was further aggravated by the inward tapering and narrowing of the luminaire toward the bottom, caused by the draft angle required to mold the luminaire in one piece. Third, the inward tapering made the luminaires more subject to rising out of the soil in cold climates where freezing and thawing cycles occurred.